This invention relates to antennas, and in particular collapsible single or multi element rhombic antennas for use in the transmission and reception of horizontally or vertically polarized electromagnetic waves.
Radio communication has been possible between United States and Great Britain since 1925 using rhombic antennas. The versatility of the rhombic antenna makes it well suited for high gain transmission and reception of radio signals. Prior art rhombic antennas used for radio frequencies were large fixed structures that required several acres of land and hundreds of feet of wire to operate. For example, U.S. Pat. No. 2,145,024 which issued to Bruce on Jan. 24, 1939, discloses the use of a plurality of rotatable and adjustable rhombic antennas to receive and transit horizontally and vertically polarized electromagnetic waves. These antennas require bulky and cumbersome support structures or frames to support the antennas. The later development of multi element or arrayed rhombic antennas only exaggerated these structural problems. With the development of "direct TV" applications, low cost, easy to install, antennas are expected to have wide markets. Therefore, it is desirable to develop a rhombic antenna which is easily installed in either a vertical or horizontal position without requiring a cumbersome support structure. It is also desirable to develop a collapsible antenna which can be easily broken down and reassembled. Such a collapsible antenna should be light weight and compact when broken down so that it can be easily transported or shipped from one location to another.
Rhombic antennas typically include a translation device mounted at a remote location outside of an enclosure delimited by the wire antenna elements. The Bruce patent discloses a translation device for summing the received signal which is mounted behind or externally to this enclosure. Modem translation devices typically include a down converter for amplifying and converting electromagnetic radiation to an analog or digital signal (an electric current) at the desired reception frequency and an impedance matching network for matching the impedance of the antenna feed to the input impedance of the translation device to produce the desired signal transmission. Such translation devices are protected from the environment by a housing and attached to the antenna elements via a transmission line and a balanced to unbalanced (balun) network. U.S. patents requiring the external mounting of a translation device in a housing positioned outside the enclosure defined between the wire antenna elements include the following: U.S. Pat. No. 5,198,831 to Burrell et al. on Mar. 30, 1993; U.S. Pat. No. 4,249,185 to De Cesari on Feb. 3, 1981; U.S. Pat. No. 4,152,708 to Boucher on May 1, 1979; U.S. Pat. No. 2,264,718 to Rust et al. on Dec. 2, 1941; U.S. Pat. No. 2,244,628 to Kotowski on Jun. 3, 1941; U.S. Pat. No. 2,194,554 to Katzin on Mar. 26, 1940; U.S. Pat. No. 2,145,024 to Bruce on Jan. 24, 1939; and U.S. Pat. No. 1,721,128 to Mathiesen on Jul. 16, 1929. The references suggest that it is necessary to mount the translation devices outside the enclosure defined by the wire antenna elements to prevent the disruption of the antenna's electric field which, in turn, would affect the wire currents and degrade the high gain characteristics. The Applicants are unaware of any prior art rhombic antennas or conductors that teach mounting the translation device inside this enclosure because of the widespread belief that the electrical field of the antenna would degrade the desired signal, thereby causing the antenna not to perform properly. However, such remote mounting outside this enclosure has several drawbacks. Assembly of such antennas is complicated and often requires multiple adjustments. Once assembled, the antennas are often physically unbalanced which restricts mounting ability. It is therefore desirable to develop a rhombic antenna that allows for the mounting of the translation device within the enclosure defined by the wire antenna elements and does not degrade the antenna performance. The translation device could be mounted in a protective housing attached to the outer surface of the antenna frame or in a weather proof cavity defined by the interior surface of the antenna frame or support structure. Such internal mounting within the enclosure provides for easier assembly of the antenna and a more compact and balanced design with low wind resistance.
Prior art teachings also suggest that antenna bandwidth or frequency response are dependent upon the antenna dimensions. As a result, adjustable rhombic antennas such as that disclosed in the Bruce patent were designed which allow for adjustment of the antenna dimensions to vary to the bandwidth. However, Applicants'invention disclosed hereinafter provides an antenna having fixed dimensions which controls the antenna bandwidth by varying the electrical distance between a segment of the wire antenna elements. Such an antenna finds application, for example, as a low cost alternative to existing parabolic antennas currently used in the wireless cable television industry.